Retrovirus vectors can be used to surely integrate genes of interest into host chromosomes. For this reason, these vectors are widely used in the field of gene therapy centering on ex vivo gene therapy protocols that target hematopoietic stem cells or peripheral blood lymphocytes. They also are widely used in the field of basic research as tools for gene expression analyses. This is because they can be used to achieve stable expression levels of foreign (inserted) genes. Usually, a culture supernatant of a producer cell is filtrated through a filter and the filtrate is used as a retrovirus vector. The filtrate may be subjected to further purification if the retrovirus vector is to be used for an ex vivo gene therapy protocol. However, there have been problems concerning the above because the purification of a virus vector is complicated and the recovery is low. No scientific literature describing the stability of a purified virus vector is found.
A culture supernatant of a retrovirus vector producer cell is usually stored after filtration through a filter in a frozen state in a deep freezer. The stability of a thawed vector in a solution state is low. The half-life has been reported to be 92 hours at 4° C., 18-64 hours at 0° C., 11-39 hours at 32° C., or 7-9 hours at 37° C. (Non-patent Document 1, Non-patent Document 2). Since the stability of a retrovirus vector is low as described above, a cryopreserved retrovirus vector is usually thawed upon use and used immediately.
A method in which a recombinant retrovirus is lyophilized and then stored is described in Patent Document 1. This method requires equipment for lyophilization, and a procedure for reconstituting the stored recombinant retrovirus upon use.
A gene transfer method in which a retrovirus is subjected to infection in the presence of a substance having a retrovirus-binding activity (in particular, a fibronectin fragment) is described in Patent Document 2, Patent Document 3 or Non-patent Document 3. The influence of such a substance on the stability of a retrovirus is unknown.    Patent Document 1: U.S. Pat. No. 5,792,643    Patent Document 2: WO 95/26200    Patent Document 3: WO 97/18318    Non-patent Document 1: McTaggart, S., Al-Rubeai, M., Biotechnol. Prog., 16(5):859-865 (2000)    Non-patent Document 2: Kaptein, L. C., et al., Gene Ther., 4(2):172-176 (1997)    Non-patent Document 3: Hanenberg, H. et al., Nat. Med., 2(8):876-882 (1996)